The invention relates to an agricultural machine as claimed in the preamble of claim 1. In particular, the invention relates to a machine for soil cultivation and/or treatment, for example a sowing machine.
FR 23 99 197 presents an agricultural implement having the features of the preamble of claim 1.
DE 195 31 172 A1 discloses a sowing machine in which a triangular reservoir container is attached to a rack which forms an equilateral triangle. A pair of main wheels is arranged at each of the corners which bound the base of the rack. Each pair of main wheels can pivot about a vertical axis which has a minimum distance of approximately 40 cm from the horizontal axis of the pair of main wheels. As a result, the pairs of main wheels are dragged along in a way similar to a shopping trolley so that they follow the direction of movement of the sowing machine.
FR 20 34 151 presents an agricultural implement which can be used, for example for cultivating beet. The implement has a rack with pivotable rear wheels. The rear wheels are connected by means of Bowden cables to a hitch which is also pivotable, and are positively steered as a function of the angular position of the hitch. This arrangement is intended to ensure, when working on sloping ground transversely to the direction of the slope, that the agricultural implement is oriented in a line with a tractor.
However, the arrangement known from DE 195 31 172 A1 has the disadvantage that when cornering, the main wheels pivot out and trace an arc with a relatively large diameter, as is indicated in FIG. 1 of DE 195 31 172 A1 by a dashed line. For this reason, it is necessary to provide an appropriately large amount of free space for the main wheels by structural means. This is problematic in particular if a large and heavy reservoir container is to be used. In this case, appropriately large and wide main wheels have to be used in order to prevent the pressure on the soil from becoming too large. In addition, if the main wheels pivot out to a large extent, it is necessary to construct a machine which is, seen in its entirety, a very large and cumbersome machine which does not permit tight cornering.
Accordingly, the object of the invention is to avoid the aforesaid problems and to provide an agricultural machine which is as compact and maneuverable as possible, in particular even when the reservoir container is large.
This object is achieved according to the invention by means of a machine having the features of claim 1. The dependent claims relate to preferred developments of the invention.
The invention is based on the basic idea of positively steering the at least one main wheel of the machine in accordance with the direction of a traction force exerted on the machine. As a result, it is possible to arrange the steering axis of the main wheel in such a way that, for example, it passes centrally through the main wheel. A steering movement about this axis requires considerably less space than the arcuate pivoting movement in the case of the machine known from DE 195 31 172 A1. In addition, the positive steering has an overall improving effect on the driving characteristics of the machine when performing tight cornering.
In the machine according to the invention, the hitch is arranged on the rack. In particular, the hitch may be embodied as an integral part of the rack or may be rigidly connected to the rack. However, the hitch is preferably pivotably arranged on the rack. The pivot axis of the hitch preferably extends approximately vertically, with the result that the hitch becomes oriented in accordance with the direction in which the machine is being dragged. This arrangement is particularly advantageous because, when cornering, it causes the point of connection between the hitch and a tractor to migrate toward the inside of the bend. As a result, when performing a tight cornering maneuver the tractor is provided with additional free space: On the other hand, if a hitch were arranged rigidly there would be the risk of the rear wheel of the tractor which is on the inside of the bend striking against the reservoir container.
In preferred refinements of the embodiments with a moveable hitch, the pivoting movement of the hitch is used to positively steer the main wheel or main wheels. This provides the aforesaid advantages with very little effort in structural terms. Preferably, the pivoting movement of the hitch is converted by a suitable steering linkage into a steering movement of the travel wheel. The steering linkage can have a plurality of connecting elements, in particular tie rods and/or connecting rods or levers. In other embodiments, the steering movement is generated by the machine being coupled to the tractor at two points. The main wheel or wheels can, however, also be positively steered by means of an electric or hydraulic device.
There is preferably a dependence (not necessarily linear) between the pivot angle of the hitch and the steering angle of the main wheel or the steering angles (not necessarily identical) of the main wheels. The steering movement preferably takes place in the same direction as the pulling angle, or in particular by approximately the same angle as the pulling angle so that particularly good cornering properties are achieved.
The reservoir container preferably tapers toward the hitch and has a triangular or trapezoidal horizontal projection at least in certain sections, in order to provide as much space as possible for cornering maneuvers of the tractor. In particular with reservoir containers which are relatively large and are thus heavy in the loaded state, the at least one main wheel is preferably provided with a wide tire in order to minimize the pressure on the soil. The tire preferably has a width of more than 50% or more than 60% of its diameter. The tire may be, for example, 0.5 m to 1.2 m (in particular 0.8 m) wide and/or measure 0.7 m to 2.0 m (in particular 1.35 m) in diameter. With such large tire dimensions, the inventive measure of positive steering is particularly important in order to prevent the wide tire or tires moving out too far.
In further preferred embodiments, at least two main wheels are provided, and the rack and/or the hitch are/is at least partially arranged between said main wheels. If the rack is relatively narrow and preferably does not protrude laterally beyond the reservoir container, the freedom of movement for cornering maneuvers of the tractor can thus be increased further. In this case it is also important that there is sufficient space between the main wheels in order to be able to guide a sufficiently flexurally rigid rack and/or a sufficiently flexurally rigid hitch between them.
In preferred embodiments, the machine has an agricultural implement which may be embodied as a soil cultivating and/or soil treatment implement and can have a plurality of support wheels. For example, the machine may be a sowing machine, the reservoir container may be a container for the seed, and the agricultural implement may have a sowing implement and an implement connected behind it, for example a curry comb or a heavy cultivator. For other applications, the reservoir container may be, for example, a liquid container or container for material which is to be spread.